THE MAIN GEOMORPHOSITES IN UMBRIA

THE MAIN GEOMORPHOSITES IN UMBRIA

Lucilia Gregori, Laura Melelli, Silvia Rapicetta & Andrea Taramelli Dipartimento di Scienze della Terra, Università degli Studi di Perugia, Piazza Università

06123 Perugia; email: [email protected]

ABSTRACT: L. Gregori et al., The main Geomorphosites in Umbria. (IT ISSN 0394-3356, 2005).The Region of Umbria region is characterised by highly different geological and geomorphological environments, giving the territory a“geomorphodiversity” as well as considerable variability among its ecosystems. The identification of potential geomorphosites is inte-resting, and is aimed not only at protecting them, but also at an appropriate management and use of the territory as well.This work attempts to provide a preliminary analysis by identifying common parameters within those numerous environments that bestcorrespond to the “geomorphosite” model, based on their historical, geomorphological and landscape characteristics. Therefore areview of the Umbria’s environments has been prepared.

RIASSUNTO: L. Gregori et al., Principi Geomorfositi in Umbria. (IT ISSN 0394-3356, 2005).La regione Umbria è caratterizzata da ambienti geologico-geomofologici profondamente diversi tra loro che conferiscono al territoriouna “geomorfodiversità” e, ovviamente, una profonda variabilità anche nell’ambito degli ecosistemi. L’identificazione dei potenziali geo-morfositi è interessante e finalizzata non solo alla loro tutela, ma anche alla corretta gestione e fruizione del loro territorio.Questo lavoro tenta una preventiva analisi individuando, attraverso parametri comuni, quei numerosi siti che, per caratteristiche stori-che, geomorfologiche e paesaggistiche, meglio rispondono al modello di “geomorfosito”. Si redige pertanto una rassegna dei sitiumbri identificabili in tale ambito. I siti individuati sono estremamente rappresentativi ed in buona parte unici nel loro genere. Alcunihanno un livello di valenza scientifica mondiale, come la “foresta fossile di Dunarobba”, o il sito di Pietrafitta, noto sia i suoi reperti fos-sili (gli elefanti di Pietrafitta) che per il ruolo chiave nella ricostruzione paleogeografia del territorio regionale. Altri siti, come il “colle diPerugia”, importante centro culturale ubicato al top di un paleoconoide, o Civita / Bagnoregio “la città che muore”, sono stati selezio-nati per la presenza, oltre che di forme o associazioni di forme di indubbia qualità didattica e scientifica, anche per la compresenza dialti valori storico-artistici e culturali.

Key words : Geomorphology, Geomorphosites, Landscape, Environment, Umbria, Italy.

Parole chiave: Geomorfologia, Geomorfositi, Paesaggio, Ambiente, Umbria, Italia.

Il QuaternarioItalian Journal of Quaternary Sciences18(1), 2005 - Volume Speciale, 91-99

1. INTRODUCTION

Central Italy is characterized by many “geologicaland geomorphological peculiarities” described in scien-tific literature as landforms, with high scientific or cultu-ral value (Fig. 1).

To this end, recent research has developed a newinsight that defines these areas as geosites or geo-morphosites (BRANCUCCI & BURLANDO, 2000; PANIZZA,1992; PANIZZA & PIACENTE, 2002a,b; POLI, 1999). Manyresearch groups (Working Group of the I.A.G.“Geomorphological Sites” and the Italian Researchproject COFIN 2001-2003 “Geosites in the Italian land-scape” with the UNESCO Working Group) are workingon the identification, management and protection ofgeomorphosites and are organizing workshops todiscuss and develop this issue ( in example the“Geomorphological Sites: research, assessment andimprovement” workshop in Modena, June 2002).

Based on the approaches currently available, theaim of this paper is to make an inventory of geo-morphosites in and near the region of Umbria.

Some features, well known in literature (CARTON etal., 1994), are used to identify the value of the “naturalresources.” Others (scientific, cultural and social eco-nomic) are assessed to define the importance of thesites from a world, national, regional and local perspec-tive (CARTON et al., 1994). Furthermore, there are limita-tions in the current approaches in describing and analy-

Fig.1 - Location map: main geomorphosites in the Umbriaregion: 1) Gubbio Basin; 2) Trasimeno Lake; 3) Perugia Paleo-Delta; 4) Subasio Mountain; 5) Colfiorito Polye; 6) PietrafittaMine; 7) Clitunno Springs; 8) Sibillini Mountains / Pian GrandePolye; 9) Orvieto “Mesa”; 10) Civita di Bagnoregio; 11)Dunarobba; 12) Marmore Falls.

Localizzazione dell’area di studio: principali geomorfositi inUmbria: 1) il Bacino di Gubbio; 2) il Lago Trasimeno; 3) ilPaleo-Delta di Perugia; 4) il Monte Subasio; 5) il Polye diColfiorito; 6) la Miniera di Pietrafitta; 7) le Fonti del Clitunno; 8) iMonti Sibillini / il Polye del Pian Grande; 9) la Mesa di Orvieto;10) Civita di Bagnoregio; 11) Dunarobba; 12) la Cascata delleMarmore.

92 L. Gregori et al.

sing the degree of hazard and the ex-post recovery andfruition activities. Thus there is a need to improve exi-sting methods and to develop new approaches. Foreach geomorphosite, some aspects, in addition to theliterature (BRANCUCCI et al., 1999), are described as con-ditions of hazard/risk situations. A better understandingof the mechanics and statistics of the geological andgeomorphological processes involved, along withincreased attention to the cultural heritage, has facilita-ted the individuation of several geomorphosites alreadyknown as important tourist resources in Umbria(GREGORI & RAPICETTA, 2001).

Geomorphosites are divided into two groups. Inthe first group, morphological characteristics are giventogether with cultural/historical and scenic values, forexample medieval villages near or over landforms; inthe second, scientific values are predominant. In thisgroup the principal attributes are the peculiarities of thegeomorphologic processes or the special nature of thelandforms and its conditions.

2. GEOMORPHOSITES AND TOWNS

2.1 The hill of Perugia: an example of a paleodeltaPerugia is an excellent example of a town built

over a fluvial paleodelta (Fig. 2). In the Plio-Pleistocenethe paleo-Tiber flowed into the ancient Lake Tiberinonear Perugia. The ancient town centre is built over theTiber paleodelta top set(CATTUTO & GREGORI,1988).

Sand and conglo-merate strata in a hori-zontal setting (top set)are found at the top ofthe hill along the mainroads of the town. Goingdownward toward thenew part of the town,clays, mud/sands andsands outcrop in themiddle part of the slope(foreset beds). At thebottom of the hill, thesedeposits are composedinstead of finer particles(mud and clays) in hori-zontal strata. The lobesof the paleodelta arerecognisable from diffe-rent observation points.The Perugia paleodelta isof both scientific and cul-tural interest. Accordingto this hypothesis the hillof Perugia is consideredan erosional residue ofLake Tiberino. The reco-gnising of the deltabrings to light differentneotectonic conditionslinked to the evolution ofLake Tiberino and thepaleo-Tiber flow direc-

tion. Furthermore, Perugia is one of the most importantcultural and historical towns in central Italy. It is not theonly example of a town situated on a fluvial paleodelta,but what makes it particular is the good state of preser-vation of the landform and the large number of points ofobservation along the hill recognisable, from top to bot-tom set beds (Fig. 3).

Some of the points of observation of paleodeltaoutcrops are situated near important historical sights inPerugia. Interesting outcrops are found at the VolumniHypogeum (2nd century BC), an Etruscan chambertomb, belonging to the Velimna family.

Another particular paleodelta outcrop sight is atthe Etruscan well (2nd- 3rd cent. BC), a marvel of engi-neering skill. The many connections between urbandevelopment and geological-geomorphological eviden-ce are the main grounds for defining the Perugia paleo-delta as a good example of a geomorphosite.

2.2 The Orvieto “mesa”The town of Orvieto is an important tourist attrac-

tion in Umbria. It is situated on a mesa derived frommorpho-selection processes (Fig. 4).

During the Middle Pleistocene/Holocene, erosionprocesses separated the “mesa” from the Alfina highplain that was the northern part of the VulsinoApparatus. The Orvieto mesa is an erosional “relic.”

The sequence outcropping on these structures isin the upper part the pyroclastic series (tuffs) from vol-

Fig. 2 – Perugia geological section: 1) calcareous bedrock; 2) marly bedrock; 3) arenaceous/marlybedrock; 4) clayey deposits; 5) sandy deposits; 6) gravel deposits (in Cattuto & Gregori, 1988).

Sezione geologica del Colle di Perugia: 1) substrato roccioso a composizione calcarea; 2) substratoroccioso a composizione marnosa; 3) substrato roccioso a composizione arenaceo/marnosa; 4) depo-siti argillosi; 5) depositi sabbiosi; 6) depositi conglomeratici (in Cattuto & Gregori, 1988).

Fig. 3 - Perugia cross section with the three delta sets (in Cattuto et al., 1995).

Sezione longitudinale del colle di Perugia con la ripartizione dei tre sets del delta (in Cattuto et al.,1995).

canic events during the Pleistocene, and in the lowerpart of the slope are the Pliocene clays (Fig. 5).

Fluvial erosion and mass movement phenomenaproduced the development of pyroclastic covering withcollapse in the upper part of the slope (where the pyro-clastic sequence outcrops) and landslides in the lowerpart (Fig. 6).

In ancient times, local populations chose to buildthe village on the upper part of the rocks, due to thegood geomechanics and morphological conditions ofthe tuff. Quarries, dovecotes, and reservoirs were dugout of the rock. Many of these can be visited. NearOrvieto, during an archaeological expedition an impor-tant site was unearthed, dating from the 6th cent. BC tothe 14th cent AD. This site, located in Campo dellaFiera, is very interesting for its relationships betweengeomorphology and archaeology (Fig. 7).

The paleogeographic evolution of this area wasreconstructed from the geologic, geomorphologic andphotogeologic study of the site (CATTUTO et al., 2002). Itwas possible to reconstruct an Etruscan building(“Tempio Federale”) located near a small lake.

93The main geomorphosites in Umbria

Fig. 4 - Orvieto “mesa” with a skyline of the Cathedral (photoby Gregori L.).

La “mesa” di Orvieto con la vista panoramica della Cattedrale(foto di Gregori L.).

Fig. 5 - Geological map of Orvieto with the pyroclastic sequen-ce outcropping at the town of Orvieto (Sheet 130 - GeologicalMap of Italy).

Carta geologica del territorio di Orvieto con la sequenza piro-clastica affiorante in corrispondenza della città di Orvieto(Foglio 130, Carta Geologica d’Italia).

Fig. 6 - Aerial photograph of the Orvieto area. Mass move-ments can be observed along the slopes. (Region of Umbria;scale: 1:33,000; photo date September - October 1977; SMApermission no. 38: 01/02/1978 execution. Photo by:Compagnia Generale Riprese aeree - Parma).

Foto aerea dell’area di Orvieto. Si possono osservare movi-menti di massa lungo i versanti (Regione dell’Umbria; (Regionedell’Umbria; scala 1:33.000; foto datata Settembre – Ottobre1977; SMA permesso n. 38: data di acquisizione 01/02/1978;foto della compagnia Generale Riprese aeree – Parma).

Fig. 7 - Archaeological site at Campo della Fiera, Orvieto (inCattuto et al., 2002). A) Pliocenic clay with tuff fragments, B)basaltic blocks along the slope.

Sito archeologico al Campo della Fiera - Orvieto (in Cattuto etal., 2002). A) Argille plioceniche con frammenti tufacei, B) bloc-chi basaltici lungo il versante.

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2.3 Civita: “The Dying Town”

The wonderfullandforms observable inOrvieto, Bardano, Lu-briano, Civita and Ba-gnoregio are the conse-quence of morphogene-tic processes (Fig. 8).

From differentobservation points onecan admire the wonderfulargillaceous crests of theCalanchi Valley (Fig. 9,Fig. 10), and the fascina-ting erosion-shapedmountains with their high cliffs (Cattuto et al., 1995).

Landslide and erosion processes cause the cliff torecede, bringing about slope degradation but creatingunique landscapes such as that of Civita - Bagnoregio,“the dying town.”

The cliff of Civita - Bagnoregio is composed of asequence divided into two parts: the lower part is a clayunit, the upper part is a pyroclastic unit subdivided intoan ignimbrite layer overlying tuff. This sequence is thecause of the mass movement phenomena constitutingthe risk for Civita. In addition, surface clay erosion pro-cesses create badlands. Consolidation activities havelessened the badlands in the landscape, but a compro-mise is necessary to preserve both the town’s infra-structures and the badlands as a typical landscape(GREGORI, 2003).

2.4 The morphological evidence of the “GubbioBasin Master Fault”

The town of Gubbio is known all over the worldfor its Corsa dei Ceri (“Candles” Race) and for its land-scape. Gubbio is located at the foot of a very high anti-cline limb (Fig. 11). River erosion cuts this fault scarpinto a number of triangular facets (Fig. 12). Theselandforms are clear evidence of an important normalfault. This master fault bounds a tectonic basin, withvarious morphological indications. The new part ofGubbio is built on an alluvial fan derived fromCamignano River sedimentation. The Camignano Rivercuts the anticline and models a beautiful diaclinal valley(CENCETTI, 1990).

3. GEOMORPHOSITES: MORPHOSITES ANDMORPHOGENETIC PROCESSES

3.1 Syn-rift BasinsMany basins are present in Umbria as the

“Gubbio Basin.” In central Italy such basins are veryfrequently grabens (CATTUTO et al., 1992). Several ofthese vast depressions are frequently called “polye”:this is due to the tectonic evolution of the area that ischaracterized by the activity of an extensional stressfield superposed on an earlier Upper Miocene contrac-tional stage.

The interplay between these processes, weathe-ring and the karstic process are the main factors con-trolling the stratigraphic and structural architecture ofthe active basins. The basin geometry of the Sibillini

L. Gregori et al.

Fig. 8 - Alfina Plateau cross section (in Cattuto et al., 2002).

Sezione longitudinale dell’Altopiano dell’Alfina (in Cattuto et al., 2002).

Fig. 9 – Civita di Bagnoregio and in the background the bad-lands landscape at the bottom of the Alfina Plateau (photo byGregori L.).

Civita (Bagnoregio) e sullo sfondo il paesaggio a calanchi albottom dell’Altopiano dell’Alfina (foto di Gregori L.).

Fig.10 - Outcast from erosion processes, shown in the circle(photo by Gregori L.)

Un testimone (contrassegnato dal cerchio) relitto di morfosele-zione (foto di Gregori L.).

mountains suggests this interpretation of tectonic evo-lution and brought to light the unique morphotypes ofsignificant scenic value.

It is possible to make a scenic tour along somebasins, from Gubbio-Gualdo to the Colfiorito plains(GREGORI, 1990) and as far as the Norcia basin and theSibillini mountains (Fig. 13).

95The main geomorphosites in Umbria

Fig. 11 – Block diagram of the Gubbio basin (original in SestiniA., in Castiglioni, 1979).

Block diagram del bacino di Gubbio (originale modificato trattoda Sestini A. in Castiglioni, 1979).

Fig. 12 - Triangular facets on the anticline limb near Gubbio(photo by Cencetti C.).

Faccette triangolari lungo il fianco dell’anticlinale di Gubbio(foto di Cencetti C.).

Fig. 13 - Foreground view of the Mt. Sibillini polye, in winterseason (photo by Paoletti A.).

Vista del polye dei Monti Sibillini durante la stagione invernale(foto di Paoletti A.).

3.2 Trasimeno Lake Lake Trasimeno (Fig. 14) is a tourist attraction in

Umbria which has enjoyed renewed popularity in recentyears. Many poets and writers have described the land-scape around Lake Trasimeno.

It is one of the laminar lakes in Italy, and is quiteshallow (almost 6 meters at the centre). Even thoughLake Trasimeno is undergoing a dry period, it is still an

Fig. 14 - Geological map of the Trasimeno Lake region (Sheet122 - Geological map of Italy).

Carta geologica dell’area del Lago Trasimeno (Foglio 122,Carta Geologica d’Italia).

important resource for fishing and for irrigating the sur-rounding farmlands.

Historically it has been defined as an alluvial lake;however, there is evidence that it is a tectonic lake. It isthe oldest tectonic lake in Italy (AMBROSETTI et al., 1989;CATTUTO & GREGORI, 1993; CATTUTO et al., 1995) whosegenesis is tied to the tectonic stretching that has invol-ved central Italy since the Pliocene, developing an olddrainage system which widens toward the north (Fig.15).

In particular, the tectonic system and its anti-Apennine activity confirm the model of the basin as atectonic depression for the drainage lines of secondarywater.

The morphologically articulated sides may hideinteresting historical-geological and/or floral-faunal par-ticularities and peculiarities. To this end a number ofscenic trails have been made: hiking trails, bicyclepaths around the lake, the routes and sites of Hannibal,guided visits to the castles on Maggiore Island andPolvese Island.

3.3 Marmore fallsThe far northeastern area of the Rieti plain, called

the “Piano delle Marmore,” is cut off by a 160-meterhigh escarpment coming from the southeast, joining thevalley at the Nera River. In this area the Velino Riverflows to the end of the Rieti depression before “esca-ping” toward the Marmore gorge.

Marmore falls (Fig. 16) is a spectacular example ofan active morphogenetic process, and is one of thehighest waterfalls in Italy. Besides, knowledge of thewaterfall’s inland, shows interesting geological-geo-morphological characteristics.

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The source of the Velino river is in a wide traverti-ne plain located at an elevation of 370 m, from whichthe its waters flow down to the Nera river valley.

The falls are essentially of artificial origin, fromRoman times; nevertheless, some authors have pointedout that a waterfall existed there before. These geologi-cal studies of the falls are mostly related to tectonicactivity and lead to the conclusion that the steepness isdue to a series of travertine prominences that dropdown toward stream in a narrow valley.

There are interesting yet little-known forms alongthe Plain of Marmore which are called “fosse.” Theseare pseudo-karstic complex landforms: a deep depres-sion with a flat floor surrounded by high slopes named“fosse” or “ weel.” They look like typically karsticmorphotypes (bowl-shaped dolinas).

The structural level is characterized by the pre-sence of numerous dolinas and/or deep “fosse” sur-rounded by spectacular travertine incrustations, a won-derful example of a pseudo-karstic process (MATTIOLI,1972; TROIANI, 1996) (Fig. 17, Fig. 18).

L. Gregori et al.

Fig. 15 - Paleogeographic evolution of Trasimeno Lake (inCattuto & Gregori, 1993); 1) Pliocene, 2) Lower Pleistocene; 3)Middle Pleistocene; 4) Upper Pleistocene.

Evoluzione paleogeografica del Lago Trasimeno (in Cattuto &Gregori, 1993); 1) Pliocene, 2) Pleistocene inferiore; 3)Pleistocene medio; 4) Pleistocene superiore.

Fig. 16 – Marmore falls (Terni), (photo by Troiani C.).

Cascata delle Marmore (Terni), (foto di Troiani C.).

Fig. 17 - “Tiberiana cavity ” in the Marmore plain (photo byTroiani C.).

La Fossa Tiberiana nel Piano di Marmore (foto di Troiani C.).

3.4 The Clitunno SpringsParticularly interesting is the site of the Clitunno

springs, near the small village of Campello sul Clitunno(Spoleto). Its springs, light blue width depressions (Fig.19) and riparian vegetation are a spectacular sight.

The depressions result from underground watersemerging through the detrital cover that covers the

base at the side of the Campello mountain (CATTUTO etal., 1995). The Clitunno springs are located at the baseof the relief, sometimes masked by detrital materials.Through them waters open one way to stand out inside“funnel-shaped cavities” covered by flourishingunderwater vegetation. These cavities are attributed tokarstic dissolution phenomena occurring probably inbedrock limestone. The cavities now function more as

“water issue” points than as absorption points.

3.5 The Mammalofauna of Pietrafitta mineThe Pietrafitta mine is located south of Lake

Trasimeno and is an important fossiliferous site. Since1960 numerous specimens of Mammalofauna in verygood shape have been discovered (Fig. 20) in thePleistocene lake of Tavernelle/Pietrafitta. This lacustrinedepression (AMBROSETTI et al., 1987) formed near thepaleodelta of the Nestore river. In the Plio-Pleistocenethis river flowed east to west, emptying into thePliocene sea near the modern town of Città della Pieve.

The Pleistocene tectonic activity, characterized bya general raising and sliding of the area towards theeast, also caused the sliding of the paleodelta and theinversion of the flow direction of the Nestore river (Fig.21).

Before the complete reversal, tectonic activity“stepped” this site toward the east and brought aboutthe formation of a depression that for approximatelyone million years created the conditions for a lake evo-lution and the development of luxuriant vegetation(lignites) and of fauna such as elephants, rhinoceroses,beavers and turtles. (Archidiskodon meridionalis,Dicerorhinus etruscus, Castor fiber, Emys orbicularis,Leptobos, Allophaiomys, etc; Ambrosetti et al., 1987).

Students and/or tourists can see many well-pre-served fossils in the Pietrafitta mine. This heavily minedsite is an exceptional testimonial of a particularly evo-cative paleoenvironmental scene.

97The main geomorphosites in Umbria

Fig. 21 – Pietrafitta basin cross section (in Ambrosetti et al., 1987).

Sezione trasversale del Bacino di Pietrafitta (in Ambrosetti et al., 1987).

Fig. 20 - Fossil remains (Archidiskodon meridionalis) in thePietrafitta mine (photo by Gregori L.).

Resti fossili (Archidiskodon meridionalis) nella miniera diPietrafitta (foto di Gregori L.).

Fig. 19 - Surfacing of underground waters at the Clitunnosprings (photo by Gregori L.).

Risorgenza delle Fonti del Clitunno (foto di Gregori L.).

Fig. 18 – Carbonatic ballstones along the “Tiberiana cavity”edge (photo by Troiani C.).

Concrezioni carbonatiche lungo la parete della Fossa Tiberiana(foto di Troiani C.).

3.6 The Dunarobba Fossil ForestThe Dunarobba Fossil Forest is one of the most

representative geomorphological sites in Umbria (Fig.22, Fig. 23), and certain extraordinary characteristicsmake it unique in the world.

In early 1970 the remains of a number of trees stillstanding in a “living position” were discovered in a claypit near Dunarobba. These were identified as a speci-men of an extinct conifer, Taxodioxylon gypsaceum,very similar to modern sequoias (AMBROSETTI et al.,1992). The trunks have a diameter of approximately 1.5meters and are 5 to 10 meters tall. The forest was pro-bably located on the shores of the ancient LakeTiberino and dates from the Pleistocene (the latestdating attributes it to approximately 1 million yearsago).

The extraordinariness of the site also depends onthe excellent state of preservation of the paleoenviron-ment existing when the trunks were buried (which pro-bably happened during a landslide and/or flood). Inaddition to conifer remains, other evidence of the entireecosystem was also preserved that supports the theoryof humid, warm climatic conditions. In addition, thetrunks not hardened by a mineralization process are stillwooden. In 1990 a monitoring system was set up andan experimental treatment method for the protectionand preservation of the trees was activated.

The Dunarobba Fossil Forest is protected as anenvironmental monument by the Region of Umbria andby the Ministry for Cultural Assets as a site ofPaleontological Interest. The site constitutes an impor-tant example from both a geomorphologic and a paleo-geographic/enivironmental viewpoint.

3.7 The “mortari” of Mt. SubasioMt. Subasio is formed by an elliptical anticline

fault along the western side. The bedrock that outcropsconsists of the Umbro-Marche sequence between theCalcare Massiccio formation and the MarnosoArenacea formation (lower Lias – Middle Miocene). Thebedrock outcrops in the old core of the anticline aslimestone and as marl in the recent part. The sequenceunits of Mt. Subasio is a seismogenetic box with a large

98 L. Gregori et al.

Fig. 22 - The Dunarobba Fossil Forest (photo by Gregori L.).

La Foresta Fossile di Dunarobba (foto di Gregori L.).

Fig. 23 - A tree trunk in the Dunarobba Fossil Forest (photo byGregori L.).

Tronchi fossili della Foresta Fossile di Dunarobba (foto diGregori L.).

Fig. 24 – Geological section of M. Subasio. 1) Alluvial deposit; 2) Scaglia rossa formation, 3, 4) Lias formations. (figure in Venturi &Rossi, 2003).

Sezione geologica del M. Subasio. 1) Depositi alluvionali; 2) Formazione della Scaglia rossa, 3, 4) Formazioni del Lias (figura tratta daVenturi & Rossi, 2003).

hinge area in the upper part having a many extensionalfracture patterns (Fig. 24).

At the top of the mountain (elevation approx. 1200meters), some deep dolinas locally known as mortai ormortari (mortars) are visible (Fig. 25).

Their shape is that of a mortaro, and popular tra-dition led to the belief that Mt. Subasio was an extinctvolcano (CATTUTO et al., 1995). These depressions aretypical examples of karstic morphogenesis and are alsoof educational and scenic importance (the “Big Mortar”has a maximum width of 280 m and a depth between50 and 70 m).

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99The main geomorphosites in Umbria

Fig. 25 - Aerial photograph of the Mt. Subasio area with “mor-tars” shown by the circles. (Region of Umbria; scale: 1:33.000;photo dated September - October 1977; SMA permission no.38: 01/02/1978 execution; Photo by: Compagnia GeneraleRiprese aeree - Parma)

Foto aerea dell’area del M. Subasio con i “mortari” contrasse-gnati dai cerchi (Regione dell’Umbria; scala 1:33.000; fotodatata Settembre – Ottobre 1977; SMA permesso n. 38: datadi acquisizione 01/02/1978; foto della compagnia GeneraleRiprese aeree – Parma).